Axle driving apparatus

ABSTRACT

An axle driving apparatus in which a hydraulic pump and a hydraulic motor which constitute a hydrostatic transmission are disposed on a center section. In a horizontal portion of the center section are provided a pair of linear oil passages in parallel to each other. A pair of arcuate ports are provided on a pump mounting surface formed on the horizontal portion of the center section. The pair of arcuate ports are substantially perpendicular with respect to the direction in which the oil passages extend. The axis of slanting movement of a movable swash plate of the hydraulic pump extends laterally of the vehicle body on which the axle driving apparatus is provided. The rotating direction of an arm provided on a control shaft for slantingly operating the movable swash plate is coincident with the operating direction of a control rod connected with a speed changing member. Thus, the link mechanism for connecting the speed changing member and the control arm for the movable swash plate is simplified.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/028,627, filed Jan. 5, 2005, allowed, which is a continuation of U.S.application Ser. No. 10/623,584, filed Jul. 22, 2003, now U.S. Pat. No.6,860,106, issued on Mar. 1, 2005, which is a continuation of U.S.application Ser. No. 09/923,329, filed Aug. 8, 2001, abandoned, which isa continuation of U.S. application Ser. No. 09/085,057, filed May 27,1998, now U.S. Pat. No. 6,314,730, issued on Nov. 13, 2001, which is adivisional of U.S. application Ser. No. 08/781,513, Jan. 9, 1997, nowU.S. Pat. No. 5,799,486, issued on Sep. 1, 1998, the entire disclosuresof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an axle driving apparatus which ishoused in a common housing with a hydrostatic transmission (hereinafterreferred to as an “HST”).

2. Related Art

U.S. Pat. Nos. 4,903,545 and 4,914,907, for example, disclose an axledriving apparatus which includes an HST, a differential gear unit andaxles interlocked with each other housed in a common housing. The HSTcomprises a hydraulic pump disposed on a horizontal portion of a centersection which is L-like-shaped and has a horizontal portion and avertical portion. A hydraulic motor is disposed on the vertical portionof the center section. The hydraulic pump and hydraulic motor arefluidly connected by a closed fluid circuit provided in the centersection. The hydraulic pump is driven by an external prime mover so asto drive the hydraulic motor to thereby drive the axles. U.S. Pat. No.5,201,692, for example, discloses providing a check valve at thenegative pressure side of the closed fluid circuit of the center sectionand at the lower portion of the center section through which oil storedin the housing is automatically sucked into the closed fluid circuit.

U.S. Pat. No. 4,903,545 discloses that in order for a pair of oilpassages constituting the closed fluid circuit to communicate simplywith a pair of arcuate ports formed on a pump mounting surface on theupper surface of the horizontal portion of the center section, eacharcuate port is disposed in parallel to the extending direction of theoil passage overlapping a substantially longitudinal center portion ofeach arcuate port with each oil passage to communicate therewith. Thesubstantially longitudinal center portion of each port, which isoverlapped by each port, is formed to directly downwardly communicatewith each oil passage.

When the arcuate ports are formed as mentioned above, a movable swashplate of the hydraulic pump is not able to slantingly rotate around itsaxis at a right angle to the axles. Hence, a control shaft forcontrolling the slanting rotation direction of the movable swash plate,when disposed at a right angle to the axis of rotation of the hydraulicpump, must be disposed perpendicular to the axles. However, a controlrod connected to a speed changing member provided on the vehicle forchanging the vehicle speed extends towards the axle driving apparatusand may be pushed or pulled longitudinally of the vehicle body, wherebythe control rod cannot be directly connected to the control shaft forthe movable swash plate. Hence, a link mechanism is required to convertthe longitudinal direction of operation to a lateral direction ofoperation.

In U.S. Pat. No. 5,094,077, the control shaft for the movable swashplate is disposed in parallel to the axis of rotation of the hydraulicpump so that such a link mechanism is not required. However, in order toconvert the horizontal movement of the swinging arm provided at theoperating shaft into a lateral movement of the movable swash plate, theutmost end of the control arm is made spherical. A pair of shaft guidemembers, each having a hemispherical recess, are provided for receivingeach spherical end of the control arm so that the control arm must beconnected to the movable swash plate through the shaft guide member,resulting in that the number of necessary parts is increased as is themanufacturing cost.

In the above-mentioned U.S. Pat. No. 4,914,907, the arcuate ports at thepump side of the center section are disposed perpendicularly to theextending direction of the oil passages respectively. As such, theoperating shaft of the movable swash plate can be disposed at a rightangle with respect to the axis of rotation of the hydraulic pump and inparallel to the axles so that the aforesaid link mechanism isunnecessary. However, since the arcuate ports and oil passagescommunicate with each other through separate oil passages formedperpendicularly with respect to said passages, the construction of thepassages is more complicated than is preferable.

Also, in U.S. Pat. No. 5,201,692, at the lower surface of the centersection are open two oil holes communicating with the closed fluidcircuit. A ball is inserted into each oil hole. A plate is mounted tothe lower surface of the center section by a plurality of bolts. Theplate is provided with openings which enable oil in the housing to flowinto the closed fluid circuit while preventing the balls from escapingfrom the holes. This check valve arrangement requires a large number ofparts, more man-power to construct and is high in manufacturing cost.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improvement in acenter section on which a hydraulic pump is mounted so that a movableswash plate of the hydraulic pump housed in a housing can be efficientlyoperated. In particular, the HST comprises a hydraulic pump and ahydraulic motor, which are individually mounted on mounting surfaces ofthe center section. The center section has a horizontal portion and avertical portion and is substantially L-like-shaped. The horizontalportion of the center section is provided with a pair of linear oilpassages which extend in parallel to each other. One end of each oilpassage communicates with one of a pair of arcuate ports provided on themotor mounting surface formed on the vertical portion of the centersection. An intermediate portion of each of the oil passagescommunicates with one of a pair of arcuate ports disposed on the pumpmounting surface formed on the horizontal portion of the center section.Whereby, two pair of arcuate ports are connected with each other forminga closed fluid circuit.

The arcuate ports on the pump mounting surface are disposedsubstantially vertically with respect to the direction in which the oilpassages extend and overlap at both ends with the respective oilpassages. One of the arcuate ports is deeper at one end so as tocommunicate with one of the oil passages. The other arcuate port isdeeper so as to communicate with the other oil passage, whereby theconstruction of the oil passages and arcuate ports is simple forcommunicating with each other so as to reduce manufacturing cost.

Since the arcuate ports are open at the pump mounting surface and extendin parallel to the direction of downward movement the vehicle body, theaxis of slanting movement of the movable swash plate for changing thedischarge direction and a discharge amount of oil from the hydraulicpump extends laterally of the vehicle body. A control shaft forslantingly operating the movable swash plate can be disposed at a rightangle to the axis of rotation of the hydraulic pump and parallel to theaxles. The rotating direction of an arm provided at the control shaftand the operating direction of a control rod connected to a speedchanging member are coincident with each other. Whereby the control rodcan be directly connected at one end thereof with a control arm for themovable swash plate so as to simplify the link mechanism.

In the case where the movable swash plate is of a cradle type such thatthe upper surface thereof is made convex to be slidable along a concaveportion formed on the inner surface of the housing, the axis of thecontrol shaft rotatably supported by the side wall of the housing ismade coincident with the center of curvature of the convex portion ofthe movable swash plate. An engaging portion of the swinging armprovided on the control shaft can be directly connected with respect toa groove in the side surface of the movable swash plate. Therebyenabling the above-mentioned shaft guide member to be omitted, so as toreduce the number of parts required. Also, the relative sliding movementof the groove in the movable swash plate to the engaging portion of theswinging arm is scarcely formed. Whereby the movable swash plate can beoperated smoothly without the need to apply excessive force.

Vertical oil holes are branched from a pair of oil passages for fluidlycoupling the hydraulic pump with the hydraulic motor and then are opentoward the lower surface of the center section. Check valves forsupplying operating oil are disposed in each oil hole and comprisecylindrical and bottomed valve casings inserted into each oil holes anda ball contained in each valve casing. The opening formed at the lowersurface of each valve casing is closed by a ball in a manner of beingfreely open or closed. The lower surface of each valve casing issupported to abut against the upper end surface of a projection formedon the inner bottom surface of the housing. Whereby, the check valve canbe simply locked.

BRIEF DESCRIPTION OF THE FIGURES

The above and further objects and features of the invention will be morefully apparent from the following detailed description when the same isread in connection with the accompanying drawings in which:

FIG. 1 is a plan view of an axle driving apparatus of the presentinvention;

FIG. 2 is a partial cross-sectional view of the same, from which anupper half housing has been removed;

FIG. 3 is a cross-sectional view looking in the direction of the arrows3-3 in FIG. 2;

FIG. 4 is a cross-sectional view looking in the direction of the arrows4-4 in FIG. 2;

FIG. 5 is a cross-sectional view looking in the direction of the arrows5-5 in FIG. 2;

FIG. 6 is a cross-sectional view looking in the direction of the arrows6-6 in FIG. 2;

FIG. 7 is a cross-sectional view looking in the direction of the arrows7-7 in FIG. 2;

FIG. 8 is a side view of a center section of the present invention;

FIG. 9 is a plan view of the same;

FIG. 10 is a cross-sectional view looking in the direction of the arrows10-10 in FIG. 8;

FIG. 11 is a cross-sectional view looking in the direction of the arrows11-11 in FIG. 9;

FIG. 12 is a cross-sectional view looking in the direction of the arrows12-12 in FIG. 9;

FIG. 13 is a cross-sectional view looking in the direction of the arrows13-13 in FIG. 9;

FIG. 14 is a cross-sectional view looking in the direction of the arrows14-14 in FIG. 9;

FIG. 15 is a cross-sectional view looking in the direction of the arrows15-15 in FIG. 9;

FIG. 16 is a cross-sectional side view of a brake unit according to thepresent invention;

FIG. 17(a) is a cross-sectional view looking in the direction of thearrows 17-17 in FIG. 16;

FIG. 17(b) is an enlarged cross-sectional view showing only a part ofthe principal portion of that shown in FIG. 17(a);

FIG. 18 is a partial perspective view of an upper wall of the upper halfhousing showing an air reservoir and a cylindrical portion;

FIG. 19 is a cross-sectional side view showing an operating mechanismfor a movable swash plate;

FIG. 20 is a partial cross-sectional front view of a part of theprincipal portion of the same;

FIG. 21 is an enlarged cross-sectional view of the principal portion ofa support for a pump shaft;

FIG. 22 a partial perspective view of the inner bottom surface of alower half housing showing projections of a check valve;

FIG. 23 is a perspective view of a modified embodiment of the same;

FIG. 24 is a cross-sectionl view of a modified valve of the presentinvention;

FIG. 25 is a cross-sectional view looking in the direction of arrows25-25 in FIG. 24;

FIG. 26 is a cross-sectional view looking in the direction of arrows26-26 in FIG. 24;

FIG. 27 is a partial sectional view of a modified embodiment of thebrake pad of the present invention;

FIG. 28 is a cross-sectional view of a modified embodiment of theby-pass mechanism of the present invention;

FIG. 29 is a detailed view of the by-pass operating arm of FIG. 28; and

FIG. 30 is a further detailed view of the same.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Explanation will first be given on the entire construction of an axledriving apparatus in accordance with FIGS. 1, 2 and 3, in which ahousing thereof is constructed by joining an upper half housing 1 and alower half housing 2 along horizontal and flat surrounding jointsurfaces. At the joint surfaces is provided a bearing for a motor shaft4. Bearings for axles 7 are shifted upwardly from the joint surfaces ofthe housing and are disposed in the upper half housing 1 to rotatablysupport axles 7. A counter shaft 26 is mounted laterally between motorshaft 4 and axles 7, and as shown in FIG. 6, is shifted downwardly fromthe joint surfaces. Thus, axles 7 are disposed in the upper half housing1 above the joint surface, counter shaft 26 is disposed in lower halfhousing 2 under the joint surface thereof; and motor shaft 4 is disposedlevel with the joint surface. Axles 7 are differentially coupled by adifferential gear unit 23. One end of each axle 7 projects laterallyfrom the housing. While these shafts and axles are interlocked with eachother through a gear train for power transmission discussed below, thehorizontal distance between the shafts is reduced, and the longitudinaldimension of the housing of the axle driving apparatus is diminished soas to be compact.

The interior of the housing is divided by an inner wall 8 into a firstchamber R1 for housing the HST and a second chamber R2 for housing atransmission gear unit for transmitting power from motor shaft 4 todifferential gear unit 23 and axles 7. Inner wall 8, as shown in FIG. 7,comprises an inner wall portion 8U which projects downwardly from theupper inner surface of housing 1 and an inner wall portion 8D whichprojects upwardly from the bottom inner surface. The end surfaces ofinner wall portions 8U and 8D are brought into contact with each otherto form inner wall 8. First and second chambers R1 and R2 are filledwith lubricating oil in common so as to form an oil sump. An airreservoir, as shown in FIGS. 7 and 8, is formed above differential gearunit 23 in upper half housing 1. On the upper surface of the housingpositioned above the air reservoir is provided an oiling lid 6 having abreather mechanism.

A cylindrical portion 1 b which is open at the upper end thereof isintegrally provided adjacent to a swollen portion formed on the upperwall of upper half housing 1 which houses therein differential gear unit23. A filter loading portion 1 c is constructed on the bottom surface ofcylindrical portion 1 b. At the lower wall and the side wall of thefilter loading portion 1 c are open communicating bores 1 d and 1 ewhich communicate with each other within cylindrical portion 1 b. An oilfilter 10 is mounted on oil filter loading portion 1 c. Oil filter 10comprises a filter body 10 a and a sealing material 10 b, such asrubber, for covering the outer peripheral surface of filter body 10 a,and partitions between bores 1 d and 1 e. The open end of cylindricalportion 1 b is closed by a lid 9. A spring 42 is interposed between oilfilter 10 and lid 9 so as to bias oil filter 10 toward filter loadingportion 1 c.

The amount of lubricating or operating oil filling the housing is set tosufficiently immerse the HST and the respective bearings in the oil. Theoil level 0L is somewhat higher than oil filter 10 so that the oil isflowable through communicating hole 1 d, oil filter 10 and communicatinghole 1 e. Accordingly, oil filling the housing is usable in common asoperating oil for the HST and lubricating oil for the gears andbearings. When the HST operates to raise the temperature of the oil andto increase the volume of the oil in first chamber R1, the oil isallowed to escape into second chamber R2. Conversely, when the HSTstops, the oil temperature and the volume of oil in first chamber R1decreases, causing oil to enter first chamber R1 from second chamber R2.At which time, any foreign object such as iron powder which can beharmful to the HST, is filtered by oil filter 10 so as to be preventedfrom entering into first chamber R1. This always keeps the oil in firstchamber R1 clean.

Within first chamber R1 is mounted a center section 5 which is L-likeshaped when viewed from the side and has a horizontal portion 500 and avertical portion 501. At the peripheral portions of horizontal portion500 are vertically open through bores 5 f at three positions as shown inFIG. 9. A mounting bolt 30 is inserted into each through bore 5 f frombelow to fix center section 5 to the inside of upper half housing 1. Onthe upper surface of horizontal portion 500 of center section 5 isformed a pump mounting surface 40. A cylinder block 16 is rotatablyslidably disposed thereon. Pistons 12 are fitted, through biasingsprings, into a plurality of cylinder bores in cylinder block 16 and arereciprocally movable. A thrust bearing 11 a of a movable swash plate 11abuts against the heads of pistons 12. An opening 11 b is provided atthe center of movable swash plate 11 so as to enable input shaft 3 toperforate therethrough. Input shaft 3 is vertically disposed and is notrelatively rotatably retained onto the axis of rotation of cylinderblock 16, thereby constituting an axial piston type hydraulic pump.Input shaft 3 projects outwardly at the upper end thereof from upperhalf housing 1. An input pulley 43 with a cooling fan 44 is fixed oninput shaft 3. Input pulley 43 receives power from a prime mover (notshown) through a belt transmitting mechanism (also not shown).

As shown in FIG. 3, at the outside surface of vertical portion 501 ofcenter section 5 is formed a motor mounting surface 41 on which acylinder block 17 is rotatably supported. A plurality of pistons 13 arefitted into a plurality of cylinder bores in cylinder block 17. Pistons13 are reciprocally movable whereby the heads thereof abut against afixed swash plate 37 which is fixedly sandwiched between upper halfhousing 1 and lower half housing 2. An output shaft 4 is horizontallydisposed on the axis of rotation of cylinder block 17 and is notrelatively rotatably retained thereto so as to constitute an axialpiston type hydraulic motor. Output shaft 4 is also rotatably supportedby a bearing bore provided on the vertical portion 501 of center section5 and by a bearing held at the joint surfaces of upper half housing 1and lower half housing 2.

A drive train for transmitting power from output shaft 4 to differentialgear unit 23 is shown in FIGS. 2 and 6. A gear 25 engageable with alarger diameter gear 24 on counter shaft 26 is provided on output shaft4 where it enters into second chamber R2. A smaller diameter gear 21 oncounter shaft 26 engages with a ring gear 22 of differential gear unit23. Smaller diameter gear 21 is cylindrical and extends in the directionof the axis of rotation of the gear. External teeth of gear 21 engagewith a central opening of larger diameter gear 24 so as to mutuallyconnect therewith. Ring gear 22 drives differential gear unit 23 so asto transmit power to left and right axles 7.

As shown in FIGS. 3, 16 and 17, a brake disc 19 is fixed onto an axialend of output shaft 4 positioned in second chamber R2. A brake pad 29 isfitted into the inside surface of upper half housing 1 opposite to oneside surface of an upper portion of brake disc 19. A brake operatingshaft 14 is horizontally disposed at the inside surface of upper halfhousing 1 opposite to the other side surface of disc 19 and perforatesinto and out of upper half housing 1 and is axially slidably supportedthereto through a cylindrical bush 15. One end surface of brake pad 29and the inner end surface of brake operating shaft 14 are opposite toeach other and sandwich therebetween brake disc 19. Brake operatingshaft 14 is supported by the housing in parallel to motor shaft 4. Abrake arm 27 is fixed to the outer end of brake operating shaft 14projecting from the housing. A spring 28 is fitted onto brake operatingshaft 14 so as to bias brake operating shaft 14 by moving the inner endsurface of shaft 14 away from brake disc 19.

On the inner end of brake operating shaft 14 which enters into thehousing is formed a flange 14 a. On the surface thereof opposite to theinside surface of the housing are provided two cam grooves 14 b whichare V-like shaped when viewed in cross section and are crescent shapedwhen viewed in elevation. Recesses 15 c are formed in the end surface ofcylindrical bush 15 so as to be opposite to cam groove 14 b. A ball 20is interposed between each recesses 15 c and each cam groove 14 b, asshown in FIG. 17(b). Because of this construction, when brake arm 27 isrotated around brake shaft 14, each ball 20 held in a recess 15 cgradually rides on cam groove 14 b from the deepest portion to thethinnest portion. Brake operating shaft 14 slides toward brake disc 19,so that the brake disc 19 is biased between the inner end surface ofbrake operating shaft 14 and brake pad 29, thereby exerting a brakingaction to output shaft 4. Also, at the outer end of cylindrical bush 15is integrally provided a radially extending flange 15 a. At flange 15 aare open elongate bores 15 b each in a circular arc around the axis ofbrake operating shaft 14. A bolt 18 is inserted into each elongate bore15 b to thereby non-rotatably fix bush 15 to the outside wall of upperhalf housing 1. Bolts 18 are unscrewed to properly rotate flange 15 aaround brake shaft 14, thereby enabling the timing of each ball 20riding along cam groove 14 b to be adjusted.

As shown in FIG. 9, a pair of arcuate ports 40 a and 40 b are open alongpump mounting surface 40 of center section 5 so that the feed oildischarged from cylinder block 16 is introduced into center section 5.As shown in FIG. 8, a pair of arcuate ports 41 a and 41 b are open onthe motor mounting surface 41 thereby introducing feed discharge oilinto center section 5 from cylinder block 17.

A first linear oil passage 5 a and a second linear oil passage 5 b aredrilled in parallel with each other, when viewed in plan, within thethick horizontal portion 500 of the center section 5 forming a closedfluid circuit for circulating operating oil between the hydraulic pumpand the hydraulic motor. In particular, as shown in FIGS. 8 and 9,arcuate ports 40 a and 40 b on pump mounting surface 40 are disposedperpendicular to the extending direction of first linear oil passage 5 aand second linear oil passage 5 b. The length of arcuate ports 40 a and40 b and the distance between first and second linear oil passages 5 aand 5 b are designed so that one end portion 40 a′ of arcuate port 40 aand one end portion 40 b′ of arcuate port 40 b overlap first linear oilpassage 5 a. The other end portion 40 a′ of arcuate port 40 a and theother end portion 40 b″ of arcuate port 40 b overlap with second linearoil passage 5 b.

As shown in FIG. 13, arcuate port 40 a is made deeper at one end portion40 a′ to communicate with first linear oil passage 5 a. The other endportion 40 a″ is thinner so as to not communicate with second linear oilpassage 5 b. As shown in FIG. 11, one end portion 40 b′ of arcuate port40 b is made so thin as to not communicate with first linear oil passage5 a. The other end portion 40 b″ of the same is made deeper tocommunicate with second linear oil passage 5 b.

As shown in FIGS. 9 and 14, first linear oil passage 5 a communicates atthe terminal portion thereof with arcuate port 41 a on motor mountingsurface 41 and at the intermediate portion with one end 40 a′ of arcuateport 40 a on pump mounting surface 40. The beginning of first linear oilpassage 5 a is closed by a plug member 64. As shown in FIGS. 9 and 15,second linear oil passage 5 b communicates at the terminal portionthereof with arcuate port 41 b on motor mounting surface 41 and at theintermediate portion with the other end 40 b″ of arcuate port 40 b onpump mounting surface 40. The beginning of second linear oil passage 5 bis closed by a plug member.

The outer end surface of each plug member 64, when the center section 5is placed in position in the housing, is opposite to the end surfaces ofprojections 2C provided on the inner wall of lower half housing 2. Evenwhen plug members 64 are subjected to pressure in first and secondlinear oil passages 5 a and 5 b, they are prevented from escaping fromcenter section 5. Thus, the variable displacement hydraulic pump andfixed displacement hydraulic motor are connected under oil pressurethrough the closed fluid circuit. In addition, when the depths ofarcuate ports 40 a and 40 b with respect to the first and second linearoil passages 5 a and 5 b are made reverse, in other words, the one endportion 40 a′ of the arcuate port 40 a is made smaller in depth so asnot to communicate with the first linear oil passage 5 a and the otherend portion 40 a″ of the same is made larger in depth so as tocommunicate with the second linear oil passage 5 b, one end portion 40b′ of arcuate port 40 b is made deeper in order to communicate withfirst linear oil passage 5 a. The other end portion 40 b″ of the same ismade thinner so as to not communicate with second linear oil passage 5b. So that even when the output rotating direction of the prime mover isreversed with respect to input shaft 3, it is possible that the outputrotation direction of the hydraulic motor is not changed.

As shown in FIGS. 5, 14 and 15, in order to fill the closed fluidcircuit with operating oil after the axle driving apparatus has beenassembled, oiling pipes 52 and 53 communicating with first and secondlinear oil passages 5 a and 5 b are disposed on the lower surface of thehorizontal surface of center section 5 and are exposed at the lower endsthereof from the outer bottom surface of lower half housing 2. The openend of each oiling pipe 52 and 53 is closed by a blind plug after theclosed fluid circuit is filled with operating oil.

As shown in FIGS. 4, 12, 14 and 15, vertical oil holes 5 c and 5 d arebranched downwardly from the intermediate portion and extend in thedirection of first and second linear oil passages 5 a and 5 b. Verticaloil holes 5 c and 5 d are open on the lower surface of horizontalportion 500 of center section 5. Check valves 54 and 55 for operatingsupply oil are disposed in the operating end of oil holes 5 c and 5 d,respectively. Check valves 54 and 55 are simply constructed by housingballs 54 b and 55 b in valve casings 54 a and 55 a, respectively. Valvecasings 54 a and 55 a are cylindrically shaped. The bottom thereof isprovided at the center of lower surfaces 54 c and 55 c with openings 54d and 55 d and form the upper inner peripheral portion of openings 54 dand 55 d into valve seats 54 e and 55 e with which balls 54 b and 55 bcome into close contact, respectively. Thus, casings 54 a and 55 ahousing balls 54 b and 55 b therein are merely contained in the oilholes 5 c and 5 d, so that openings 54 d and 55 d are closed by theweight of balls 54 b and 55 b and pressure in first and second linearoil passages 5 a and 5 b respectively, thereby providing check valveswhich are simple in construction and are inexpensive to produce.

Since valve casings 54 a and 55 a, when inserted into oil holes 5 c and5 d, have a potential of being subjected to the pressure of first andsecond linear oil passages 5 a and 5 b so as to downwardly escape fromoil holes 5 c and 5 d, as shown in FIGS. 4 and 22, on the inner bottomsurface of lower half housing 2 are integrally formed upwardlyprojecting projections 2 a which have sufficient length to abut againstlower surfaces 54 c and 55 c of valve casings 54 a and 55 a. Theprojections 2 a are formed to meet outer diameters of valve casings 54 aand 55 a. An annular oil filter 56 is disposed on the inner bottomsurface of lower half housing 2 in a manner of surrounding projections 2a. Oil filter 56 is covered on the upper and lower end surfaces thereofwith a sealing material. The lower surface of center section 5 isbrought into close contact with the inner bottom surface of lower halfhousing 2, thereby partitioning the interior of oil filter 56 from theexterior thereof, whereby the oil is always kept clean. Oil filter 56 ismade of an annular piece of molded porous material, such as cellulose ora foaming agent, or of a mesh comprised of fine knitted iron wires. Eachprojection 2 a is cutout in the side wall downwardly from the upper endin several positions (there are two projections in this embodiment) soas to form oil passages 2 b. Oil in the oil sump may be guided toopenings 54 d and 55 d in valve casings 54 a and 55 a through the oilpassages 2 b. When operating oil flows in the closed fluid circuit atthe negative pressure side thereof, ball 54 b or 55 b of check valve 54or 55 is subjected to negative pressure causing the ball to rises andfloat, so that the clean oil stored in the oil filter 56 is suppliedinto openings 54 d and 55 d in the valve casing 54 a or 55 a through theoil passages 2 b in projection 2 a and into first linear oil passage 5 aor second linear oil passage 5 b at the negative pressure side throughoil hole 5 c or 5 d.

A modified embodiment of projection 2 a may be formed as shown in FIG.23. In other words, projection 2 a′ is formed as a single elongatecylindrical member of external shape striding across both valve casings54 a and 55 a. The lower surfaces 54 c and 55 c of valve casings 54 aand 55 a abut against the upper end surface of the projection so as toprovide an oil passage 2 b′ from the upper end edge to the side wall.Projections 2 a and 2 a′ can be cast simultaneously when molding lowerhalf housing 2. In this modified embodiment, the plate element forconstituting the check valve required to be screwably fixed to the lowersurface of center section 5 can be omitted, thereby the construction ofthe check valves may be simplified so as to reduce the number of partsand the manufacturing cost.

As shown in FIGS. 3, 5 and 9, a by-pass operating arm 60 is disposed onupper half housing 1 so as to open first and second linear oil passages5 a and 5 b into the oil sump for enabling the axles to be idle when thevehicle is hauled. In particular, by-pass operating arm 60 is fixed atthe base thereof to an upper end of a by-pass shaft 61 which isvertically and pivotally supported to the upper wall of upper halfhousing 1. By-pass shaft 61 extends at the lower end thereof intovertical portion 501 of center section 5 so as to form at the sidesurface a flat surface 61 a. A through bore 5 e (see FIG. 8) is open onmotor mounting surface 41 of center section 5, slightly above the centerthereof and between arcuate ports 41 a and 41 b. A push pin 62 isslidably supported into through bore 5 e in the direction of the axis ofrotation of cylinder block 17 and can abut at one end against the rearsurface of cylinder block 17 in close contact with motor mountingsurface 41 and at the other end against flat surface 61 a of by-passshaft 61.

In such a construction, when an operator operates by-pass operating arm60 outside of the housing for hauling the vehicle, by-pass shaft 61 isrotated and flat surface 61 a at the lower end thereof presses push pin62 toward cylinder block 17 so that push pin 62 releases the closecontact of motor mounting surface 41 with cylinder block 17. First andsecond linear oil passages 5 a and 5 b communicate with the oil sump inthe housing through arcuate ports 41 a and 41 b, thereby enabling outputshaft 4 and axles 7 to be idle.

Pump shaft 3, as shown in FIG. 3, is rotatably supported at the lowerend thereof by a central portion of mounting surface 40 and at the upperportion through a bearing 45 in a bearing support 1 f formed in theupper wall of the housing. Conventionally, on the inner peripheralsurface of bearing support 1 f for fitting therein bearing 45, aretaining groove for fitting therein a locking ring for bearing 45 hasbeen machined. Such machining, however, takes much time and laborcausing a high manufacturing cost. In this embodiment, as shown in FIG.21, when upper half housing 1 is molded, bearing 45 and sealing member46 are fitted onto pump shaft 3 and are inserted into bearing support Ifdirectly after being cast and is not machined. The outer periphery ofsealing member 46 is coated with a ring 47 of sintered material orsynthetic resin, and a washer or a plate 48 fitted by mounting bolts 49to the upper surface of bearing support if is brought into contact withthe upper end surface of ring 47 so as to lock bearing 45 in place. Inaddition, an O-ring 50 is interposed between the outer periphery of ring47 and the inner periphery of bearing support 1 f to seal them forpreventing oil from leaking therebetween.

The piston abutting surface of movable swash plate 11 is slantinglyoperated with respect to the axis of rotation of cylinder block 16 tothereby change the amount and direction of oil discharged from thehydraulic pump. As shown in FIG. 19, at the rear surface of movableswash plate 11 is formed a convex portion 11 c. At the inner surface ofthe upper wall of upper half housing 1 is formed a concave portionsimilar in shape to convex portion 11 c. Movable swash plate 11 iscradled to slide along the concave portion of upper half housing 1 whenit is slantingly moved. Movable swash plate 11 may be of a trunnion typehaving shafts at both lateral sides thereof. The axis of slantingmovement of movable swash plate 11 is positioned on the center ofcurvature X of convex portion 11 c and extends perpendicular to theextending direction of arcuate ports 40 a and 40 b open on pump mountingsurface 40 of center section 5. Thus, the axis extends in parallel tooutput shaft 4 and axles 7.

Movable swash plate 11 is constructed for slanting movement. As shown inFIGS. 19 and 20, a control shaft 35 is disposed on the side wall ofupper half housing 1 positioned on a phantom extension line of thecenter of curvature X of the inner peripheral surface of convex portion11 c and is rotatably supported on cylindrical bush 51. As shown inFIGS. 2 and 3, cylindrical bush 51 is press-fitted into an insertionbore 1 g open in the side wall of upper half housing 1. The reason forthis is that when insertion bore 1 g is cast when upper half housing 1is molded, a draft is formed, so that it is difficult to directlysupport control shaft 35 in insertion bore 1 g while keeping the oiltight using cylindrical bush 51. In addition, an O-ring 59 is interposedfor sealing between the outer peripheral surface of cylindrical bush 51and the inner peripheral surface of insertion bore 1 g. Cylindrical bush51 is used to omit the need to machine insertion bore 1 g, therebydecreasing the manufacturing cost of upper half housing 1.

Onto the outer end of the control shaft 35 outside of the housing isfixed a control arm 38 to enable movable swash plate 11 to be slantinglyoperated from the exterior of the housing. Control arm 38 is connectedthrough a control rod (not shown) and may be pushed or pulledlongitudinally to control the vehicle with respect to a speed changingmember (not shown), such as a lever or a pedal (not shown) provided onthe vehicle. A swinging arm 39 is fixed to the inner end of controlshaft 35 within the housing, and comprises a first arm 39 a an a secondarm 39 b which radially extend from shaft 35. From the utmost end offirst arm 39 a projects an engaging portion 39 a′ extending in parallelto control shaft 35. From the utmost end of second arm 39 b projects anengaging portion 39 b′ extending in parallel to control shaft 35.Engaging portions 39 a′ and 39 b′ project opposite to each other.Engaging portion 39 b′ is directly connected to a groove lid provided inthe side surface of movable swash plate 11. Groove 1 d is formed betweena pair of engaging projections 1 e disposed on the side surface ofmovable swash plate 11 and are longitudinally spaced at a predeterminedinterval.

In such construction, when control arm 38 is rotated longitudinally ofthe vehicle body, swinging arm 39 rotates longitudinally around controlshaft 35 to enable movable swash plate 11 to be slantingly operated andthe hydraulic pump to be operated to change its output. In addition, inthis embodiment, second arm 39 b is provided at the utmost end thereofwith engaging portion of 39 b′, however, second arm 39 b may enter atthe utmost end thereof directly into groove 1 d between engagingprojections 1 e. Since the arm of control shaft 35 coincides with thecenter of curvature X of convex portion 11 c, engaging portion 1 e andengaging portion 39 b′, no matter what slanting position moveable swashplate 11 is kept in, always abut against each other in one point.Whereby there is no need to provide any shaft guide member as allowingrelative slide between engaging portion 39 b′ and groove lid. Hence, itis easy to manage the dimension between engaging projections 11 e andengaging portion 9 b′ and the neutral position of movable swash plate 11can be easily obtained.

As shown in FIG. 20, a coiled neutral return spring 31 is fitted ontocylindrical bush 51. Both ends of return spring 31 are crossed to extendin the direction of first arm 39 a and sandwich therebetween aneccentric shaft 33 mounted to the inside wall of upper half housing 1near control shaft 35 and engaging portion 39 a′ of swinging arm 39.Accordingly, when control arm 38 is turned for changing the vehiclespeed, swinging arm 39 is turned and the one end of neutral returnspring 31 is moved away from the other end, which is received byeccentric shaft 33, thereby applying to control arm 38 a biasing forceto return to the neutral position. When the operating force to the speedchanging member is released, a restoring force generated at one end ofneutral return spring 31 returns engaging portion 39 a″ toward eccentricshaft 33 so as to hold control arm 38 in the neutral position. Theextension of eccentric shaft 33 outside of the housing creates anadjusting screw so as to enable eccentric shaft 33 to be rotatablyshifted, whereby swinging arm 39 can be shifted to an optional positionaround control shaft 35 so that movable swash plate 11 is adjustable tobe in the accurate neutral position.

As mentioned above, the present invention is designed so that thearcuate ports on the pump mounting surface formed on the horizontalportion of the center section are open perpendicular to the direction inwhich the oil passages extend. Each end of the arcuate ports overlapwith an oil passage. One end of one arcuate port is made deep tocommunicate with one of the oil passages. One end of the other arcuateport is made deep to communicate with the other oil passage. Whereby,the arcuate ports can simply communicate with each other and the centersection can be inexpensively produced. The arcuate ports open on thepump mounting surface are oriented in the direction of forward movement.The axis of slanting movement of the movable swash plate is made toextend laterally of the vehicle body, whereby the control shaft forslantingly moving the movable swash plate can be disposed perpendicularto the axis of rotation of the hydraulic pump and in parallel to theaxles. Hence, the rotating direction of the arm provided on the controlshaft and the operating direction of the control rod connected with thespeed changing member are coincident with each other so as to enable thelink mechanism for connecting the speed changing member and the controlarm for the movable swash plate to be simplified.

Since the axis of the control shaft for rotating the movable swash platecoincides with the center of curvature of the concave portion of thecradle type movable swash plate, the engaging portion at the swingingarm provided on the control shaft with respect to the groove at the sidesurface of the movable swash plate can simply be constructed, therebyenabling the shaft guide member to be omitted and the number of parts tobe reduced. Also, the engaging portion of the swinging arm scarcely hasrelative slide with respect to the groove in the movable swash plate,whereby the movable swash plate can smoothly slantingly be operatedwithout applying an excessive force, resulting in an improvement inoperability.

Also, oil holes are branched from a pair of oil passages in the centersection for fluidly coupling the hydraulic pump and hydraulic motor areopen at the lower surface of the center section. The check valvescomprising the valve casing and the balls therein and for supplying theoperating oil are inserted into the oil holes. The valve casings aresupported at the lower surface by projections provided on the innerbottom surface of the housing, whereby the check valves can be extremelysimply constructed so as to lower the manufacturing cost. Theprojections are simple in shape and can be formed simultaneously whenthe housing is manufactured.

An alternative embodiment of the check valve of the present invention isshown in FIGS. 24, 25 and 26, in which similar reference numerals havebeen used to refer to similar elements described above. In thisembodiment, a hole 54 f in valve 54, which is a continuation of opening54 b, has a diameter which is larger than that of ball 54 b. On theinner surface of hole 54 f is formed three projections 54 g (See FIG.25) which contact with the outer diameter of ball 54 b. Projections 54 gextend in the direction of the longitudinal axis of valve casing 54 aand are spaced equally apart from each other inner circle. When oil hole5 c is subject to negative pressure, ball 54 b separates from valve seat54 e causing oil to flow from the lower portion to the upper portion ofvalve 54. Projections 54 g maintain ball 54 b in a straight pathpreventing it from shaking within valve casing 54 a as it rises abovevalve seat 54 e.

A stopper plate 54 h is provided at the top of valve casing 54 a toprevent ball 54 b from flowing out of valve casing 54 a when the valveis released to permit oil to flow through valve 54. The outer diameterof stopper plate 54 h has three indentations which permit the oil tocirculate smoothly through stopper plate 54 h. A second opening 54 j isformed at the lower end of valve casing 54 a to increase the suctionarea of opening 54 d.

An alternative embodiment of the brake pad of the present invention isshown in FIG. 27, in which similar reference numerals have been used torefer to similar elements described above. In this embodiment, brake pad29 is formed in an upside-down L-like shape when viewed in plan and isprovided in a similar shaped cavity formed in upper half housing 1. Theupper, horizontal portion of brake pad 29 contacts the top, rear andside walls of the cavity. The end of the lower, vertical portion ofbrake pad 29 is coextensive with the joint surface of upper housing 1and lower housing 2 and is in contact with a projection 2 a formed onthe inner surface of lower housing 2. During assembly, brake pad 29 isinserted into the cavity formed in upper housing 1 before upper housing1 and lower housing 2 are joined. As a result, brake pad 29 isnon-rotatably fixed in the cavity.

An alternative embodiment of the by-pass operating arm of the presentinvention is shown in FIGS. 28, 29 and 30 in which similar referencenumerals have been used to refer to similar elements described above. Asdescribed above, when by-pass shaft 61 is rotated about 35 , motorcylinder block 17 rises from motor mounting surface 41 of center section5. Notches 600, 601, 602 and 603 are formed in the bottom surface ofby-pass arm 60. Notches 600, 601, 602 and 603 are each of varying depthand are connected to form a continuous circular arc in by-pass arm 60. Aunitary projection 1 f extends upwardly from upper housing 1. The topend of projection 1 f fits into notches 600, 601, 602 and 603. Notches600 and 603 are disposed at the ends of the circular arc and are ofequal depth. Notch 601 is disposed adjacent to and is shallower thannotch 600. Notch 602 is disposed between notch 601 and notch 603. Notch602 is deeper then notch 601, but is shallower than notch 603.

When projection 1 f is fitted in notch 600, cylinder block 17 is held ina “closed position” in close contact with motor mounting surface 41.Because by-pass arm 60 is made of synthetic resin material, it bendswhich permits arm 60 to be shifted between notches 600, 601, 602 and603. While by-pass arm 60 is turning 35, projection 1 f is shifted fromnotch 600 to shallower notch 601 which puts resistance on the arm givingthe operator the feeling that arm 60 is heavy. When Projection 1 f isthen shifted to notch 603 through notch 602, cylinder block 17 is movedto the “open position” and rises from motor mounting surface 41. Aprojection 60 a is formed at each end of arm 60 and contacts the sidesurface of projection 1 f to prevent it from being shifted beyond notch600 or notch 603. A plate spring 70 is provided between an inner uppersurface of upper housing 1 and by-pass shaft 61. Plate spring 70 biasesby-pass arm 60 and by-pass shaft 61 downwardly to eliminate play and tomaintain projection 1 f in one of notches 600, 601, 602 and 603.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purpose only,and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the invention as definedin the following claims.

1. An axle driving apparatus comprising: a common housing; an axledisposed in the housing; a fluid sump formed in the housing; a hydraulicpump disposed in the housing; a hydraulic motor disposed in the housing;a center section disposed in the housing, the center section includingupper and lower opposite horizontal surfaces; a pair of arcuate portsopened on the upper horizontal surface onto which the hydraulic pump isfitted; a pair of fluid passages formed in the center section betweenthe upper and lower horizontal surfaces so as to fluidly connect therespective arcuate ports to the hydraulic motor; a pair of holes openedon the lower horizontal surface, and connected to the respective fluidpassages; a pair of check valve casings incorporating respective checkvalves fitted into the respective holes so as to be prevented fromescaping from the respective holes, wherein each of the check valves isopened to allow only a flow from the fluid sump to the correspondingfluid passage; and a fluid filter disposed in the fluid sump in thehousing so as to cover the check valve casings.
 2. The axle drivingapparatus as set forth in claim 1, wherein the fluid filter is acylindrical member having a pair of opposite openings, one of which isfitted to the lower horizontal surface of the center section, and theother of which is fitted to a bottom portion of the housing.
 3. The axledriving apparatus as set forth in claim 1, wherein the check valvecasings are supported by an upward projection formed on the bottomportion of the housing so as to be prevented from escaping from therespective holes.